Robert Geoffrey Trease, writer: born Nottingham 11 August 1909; Chairman, Children's Writer's Group 1962-63; Chairman, Society of Authors 1972-73, member of Council 1974-98; FRSL 1979; married 1933 Marian Boyer (died 1989; one daughter); died Bath 27 January 1998.

Geoffrey Trease published his 100th book in 1990 and wrote regularly until last winter. His best-known book is probably Cue for Treason (1940).

He was a born writer. He himself recalled that his first writing was in a fat desk-diary, a handsome wine-and-spirit trade production his father had brought home from his office in Nottingham. Young Geoffrey was given it to scribble in and, as he "wrote", he made up stories, muttering the words he did not yet know how to write.

His own childhood reading was dominated by the tastes of his older brothers - Ballantyne, Henty, the Boy's Own Paper. As a child he never read Carroll, Beatrix Potter or E. Nesbit. Over the years he tried every sort of writing except fantasy, for adults as well as children: biography, plays (he was devoted to the theatre), travel books. But it is as a historical novelist for children he will be best remembered. He should not be confused with another fine prolific historical novelist born just two years later: Henry Treece. Treece died in 1966. Geoffrey Trease was one of the last survivors of the generation of children's writers who came to prominence before the Second World War.

When he started writing it was common for an author to sell his copyright "for a single payment of perhaps fifty pounds", he wrote.

There was nothing to be done then but begin another, and then another. He was on a treadmill. It was small wonder that so much of children's literature was hackwork.

It was, in fact, not literature at all. Moreover it was "sodden", as Orwell put it, "in the worst illusions of 1910". This was only unimportant if you thought what was read in childhood left no impression behind.

Trease quoted Boswell saying, "He who pleases children will be remembered with pleasure by men." There must be many readers whose interest in history was originally fired by reading Trease, and some whose knowledge of Garibaldi or King Alfred comes entirely from reading Follow My Black Plume or Mist over Athelney 30 or 40 years ago.

Geoffrey Trease earned his first half-guinea as a writer at the age of 13 with an article on "Amateur Journalism". Five years later he won a scholarship to read Greats at Queen's College, Oxford - but dropped out after a year to work at a settlement in the East End of London. As a writer, he started out as a passionate young socialist determined to overthrow the sentimental romanticism of historical fiction at the time. "Some of the merriment should be taken out of Merrie England," he wrote. "The story would gain not lose. You could stand Henty on his head . . ."

Bows Against the Barons (1934), his very first book, is a milestone in the history of children's literature. His Robin Hood cries out: "There are only two classes, masters and men, haves and have-nots." There was never any doubt which side Trease was on.

Trease was never a Communist but his approach was such that his radical early books sold huge numbers in the Soviet Union - as many as 100,000 of the first. Geoffrey and his beloved wife, Marian, spent a happy Russian summer in 1935 living on royalties that could not be taken out of the country. It was a setting he was to use in White Nights of St Petersburg (1967), a story of the Bolshevik revolution, written when he was no longer the ardent political propagandist he had been.

He came to believe it was wrong "to press party politics on readers too immature to argue with him", though of course his books remained permeated with his own liberal values as he wrote, for instance, of anti-Semitism in Edward I's England or of the French Revolution. (An indication of the success of Thunder at Valmy, 1960, was that it was translated into French.)

From the beginning, Trease did away with gadzookery and varlets crying "Zounds" or "Prithee". His Sherwood outlaws spoke as ordinary human beings, not knowing Robert Graves's Romans were doing the same thing. (I, Claudius, too, was first published in 1934.)

Trease was also innovatory in introducing girls as co-partners in his stories. Trease's children venture into danger together and the association is usually historically plausible. Trease rarely made mistakes. He used to tell a story against himself - how he took great pains, as he always did, to get things right in his Anglo-Saxon story, tracing the characters' journey along the Fosse Way with a map of Roman Britain beside him, only to slip up and have them sup on rabbit meat. No publisher's reader or reviewer noticed, but a small boy in Aberdeen wrote to point out that rabbits reached England only with the Normans.

I first met Geoffrey Trease nearly 50 years ago, when he visited my girls' grammar school in Barnet. I was 17 and I chaired his lecture on "The Birth of a Book". "He was very decent to me when I talked to him," I wrote in my diary at the time. Geoffrey was always decent to everybody. He and his books were much loved. In recent years, at more than one Guardian Children's Fiction Prize lunch I was delighted to be able to introduce to him ardent readers of his, amazed at the chance of meeting him so many years after they had first enjoyed his books. Sometimes they were surprised he was still alive, though anyone in close touch with the children's book world know Trease continued regularly to publish. Indeed his 1992 Roumanian story Song for a Tattered Flag was one of his most successful books.

I told him once in a letter, having come across my ancient diary entry, that I'd commented, as a priggish schoolgirl, that he "treated writing as a business rather than a vocation". He was justifiably moved to tell me to turn again to his autobiography (A Whiff of Burnt Boats, 1971, followed in 1974 by Laughter at the Door), where he writes continually (and entertainingly) of the struggle it was to make a living as a writer. At that period he did a great deal of talking, not only about his books. For instance, his diary recorded in one fortnight in 1947 eight talks, including one at Balliol ("Is Russia Rationalist?") and one in the Conway Hall on "India's Problem: Race or Religion?" (He had spent part of the war in India in the Educational Corps.)

He said he "could not afford to miss a guinea" or a chance to make his books known. But, he told me, "hand on heart",

I have never written anything with any calculated incentive in cash terms. And I know, in my old age, that my writing is a vocation, for - my tastes and responsibilities being very modest - I don't need the money. I could stop tonight, but as you know I don't. Anything but.

He was a compulsive writer. It gave him some satisfaction to celebrate his 100th book and to look at the long shelves of his lifetime's work, many of the titles translated into a wide variety of languages. At the end of his life, the shelves were in a "modest" bungalow near Bath to which he and his wife moved from their lovely house at Colwall near Malvern, not long before Marian's death, to be near their daughter Jocelyn and her family. It was Jocelyn Payne who was his great support in his last years, helping him through months of crippling pain and encouraging him to complete a third volume of autobiography, as yet unpublished.

In 1949, at a time when there was extremely little written about children's books, Geoffrey Trease published a lively survey, Tales out Of School. The title is significant; Trease was himself always reluctant to be regarded primarily as a teacher's aid. He was, however, pleased to be taken seriously, as Margaret Meek did in her 1960 Bodley Head Monograph, Geoffrey Trease. The dedication of Trease's survey is significant too: "In memory of My Father, who loved a good yarn." If Trease's own stories were sometimes more than mere good yarns, it is certainly as a storyteller - and as a good man - that he will be long remembered.